Field of the Disclosure
This disclosure relates to an improved electrostatic filtration system and methods for the system's use for the removal of contaminants from a dielectric fluid.
Description of the Prior Art
Early prior art filters include filters for removing particles from various dielectric fluids such as lubricating oils and hydraulic fluids by employing mechanical filtration. When mechanical filtration is employed to filter very fine particles, i.e., below about 3 microns, difficulties may be encountered because these relatively small particles may require large bulk and volume filters to avoid significant system pressure drops caused by the necessarily small openings in the filter media.
Several earlier patents by Donald Thompson replaced mechanical filters for fine particle filtration of dielectric fluids with electrostatic filters where the fluid is passed through a number of perforated electrodes which are alternately charged with relatively high positive and negative direct current (D.C.) voltages.
Porous filter media was placed between the charged plates for trapping the particles and extends across the entire internal cross-sectional area of the filter. It appears that the particles when subjected to the electric fields created by the application of a voltage to the charged plates were captured by one of two possible ways. The filter media itself may be charged, with the particles being attracted to the filter media itself. More likely, however, the particles were charged either positively or negatively depending on their composition and the oppositely charged particles were attracted to each other and eventually flow together into agglomerate (clumps) which would be large enough to be trapped in the filter media. When enough clumps form to effectively block the filter or produce an undesirable pressure drop, the filter media would be replaced.
This can result in the required use of a very large diameter filter or a large number of filters when higher flow rates are desired. Accordingly, a continuing effort was directed to the development of improved electrostatic filters which led to the issuance of the U.S. Pat. No. 5,785,834 ('834) issued Jul. 28, 1998, U.S. Pat. No. 6,129,829 (829) issued Oct. 10, 2000, U.S. Pat. No. 6,284,118 ('118) issued Sep. 4, 2001, and U.S. Pat. No. 6,576,107 ('107) issued Jun. 10, 2003, all issued to Donald E. Thompson. The '107 series of patents are all based upon the US 2001/0037941 patent application specification. This series of patents (referred to as the Thomson '107 family) are hereby incorporated in their entirety by reference. The U.S. Pat. No. 6,576,107 patent is owned by the Assignee/Applicant of the instant application.
The '834, '829, '118 and '107 patents overcame difficulties with earlier patents where the flow of the contaminated fluid through the filter was axial and utilized electrodes separated by layers of filter media. The electrodes were alternately oppositely charged with the filtration process taking place by flowing the contaminated fluid upwardly through the electrodes and the filter media between the plates.
However, the design of the Thompson '107 family of patents developed an arcing problem that created ohmic resistance paths between the high voltage source and the filter elements. These areas of ohmic resistance reduce the overall efficiency of the filter.
To illustrate the cause of these areas of ohmic resistance, FIG. 4 of the '107 family of Thomson patents illustrates a potential cause of this arcing problem is illustrated herein as prior art (FIG. 1 herein).
The discussion of FIG. 1 herein (FIG. 4 of Thompson '107 family) appears at Column 4 Line 61 to Column 5 Line 35 in each of the Thompson '107 family.
As discussed in the Thompson '107 family specifications, FIG. 1 illustrates the '107 family method of transfer of electricity utilizing two charged electrical rods (One Positive and One Negative). This is how the '107 family of filters transfers its electricity from the bottom of the housing to the filter elements themselves. It utilizes insulator-charged springs to transfer the high voltage field up through the filter. However, this created a problem in that electrical arcing developed, creating and undesired ohmic resistance paths that would accumulate between the plates due to the lack of a solid connection point to transfer the voltage. A small arcing burn would be left on the plates at each point where the springs and plates were in contact, indicating that there was not sufficient contact with the conductive surface to allow high voltage electricity to flow efficiently through the filter elements.
There is a need for an electrostatic filtration device that can efficiently transfer the high voltage power to its charged plates without arcing developing at contact points between the source and the plates.
A second example of prior art is illustrated by U.S. Pat. No. 8,021,523 ('523) by Jarvis entitled “Apparatus and Method for Electrostatic Filtration of Fluids” issued on Sep. 20, 2011 and is hereby incorporated by reference in its entirety herein.
FIGS. 4, 4A, 4B and 9 from '523 patent are copied herein as prior art in FIGS. 2, 2A, 2B 2C. The discussion of FIGS. 2, 2A, 2B 2C is found in the '523 patent specification between: Column 10 Line 36 to Column 10 Line 45; between Column 11 Line 11 to Column 12 Line 67; and between Column 15 Line 3 to Column 15 Line 25.
The '523 device may have been an improvement over the Thompson '107 series, but the Applicant has concerns that arcing may well occur in at least two areas of the '523 design. Firstly, the use of multiple connecting elements such as the series of short metal rod sections 505 screwed together may be a haven for arcing, due to lack of total contact between the first and the second short metal rod sections 505. Such resistance burrs reduce the flow of high voltage and reduces the efficiency of the device. A second area of concern is the dependence on the contact of the negatively chargeable plates 420 which have an outer diameter that is machined to be only slightly smaller than the inner diameter of electrically conductive housing 320. In this fashion, each negatively chargeable plate 420 may make electrical contact with the inner wall of electrically conductive housing 320. Areas of non-contact by negatively chargeable plate 420 with the inner wall of electrically conductive housing 320 may well create resistance burrs that reduce the flow of high voltage and the efficiency of the device.
A separate concern for the '523 design is the flow of fluids as described in FIG. 2C. FIG. 2C illustrates a series flow of the contaminated fluid. When reviewing FIG. 2C it appears that this is a series flow of the contaminated fluid through the filtration cartridge. As shown in FIG. 2C, the fluid to be treated will flow upwards as it is introduced into the bottom of the cartridge, it will rise until it begins to contact the bottom of positively chargeable plates 430 and flow towards the outer wall of the conductive housing 320. Upon reaching the outer wall of housing 320, the fluid to be treated will eventually rise up, around, and over positively chargeable plates 430 until it contacts the lower surface of negatively chargeable plates 420 where it will then flow radially inward until it flows through the large opening in the center of negatively chargeable plates 420. The fluid to be treated will then flow through the opening. This process continues as the fluid to be treated is continually pumped into the bottom of housing 320, passing through filtration media 440 as it rises. The process will repeat until the fluid to be treated has passed over or through each layer of filtration cartridge. However, if any one of these filtration media 440 becomes clogged, the flow may stop, requiring replacement of the entire filtration cartridge. The first layer of filter media will be doing the mass extraction of polar material and may blind (clog) the media very quickly.
While both the Thompson '107 series of patents and the '523 patent may have made progress in the theoretical technology of electrostatic filtration, there is still a need for an electrostatic filtration design that is not subject to arcing, resistance burns and/or the risk of fluid flow stoppage, caused by blinding (clogging) of any single layer of the filter media.